Making 2-way earphone adapter for portable MP3/DVD player?

[Lobster]

The acquisition of a portable DVD player made a massive difference to my sanity on a recent long driving trip - perfect peace from the 3 kids in the back seat for hours and hours! Only drawback was the soundtrack from the machine itself, which stopped SWMBO and me from listening to CDs in the front.

What's needed, of course, is for the three of them to be able to listen to the DVD player on headphones; unfortunately there's only one output. How can I split this three ways? I'm envisaging making a small box with three earphone sockets connected to a lead with an earphone plug on the end; but I'm assuming it's not just a case of wiring up the three sockets in parallel? Presumably the sound would be too quiet and/or it could damage the player by the impedance being wrong?

I can't believe that such gizmos aren't readily available off the shelf, but I can't find one!

David

[Andy Dingley]

Should work fine (I have a triple adapter like this already, made neatly into a moulded plug). The output stage just isn't that fussy about exact impedance. The volume will obviously drop by a few dB, but I doubt you'll even notice.

[Dave Plowman (News)]

Think that's because you've hit the nail on the head - most walkman type headphones are 32 ohms, and 3 in parallel probably wouldn't go loud enough.

You can get headphones with a higher impedance, but these tend to be rather expensive.

But if you're making something, Maplin do a chip which is a stereo headphone amp.

TDA2822M at 1.49 gbp. You'd need a few other bits and pieces - but three of these each with an individual volume control wouldn't break the bank.

It has supply voltage range of 1.8-15 volts so could be run off either the car battery or dry cells.

I've got the spec sheet here in PDF form which I could send to you. It gives a selection of suitable circuits and applications.

[Andy Mckenzie]

Maplins do a 3.5mm Stereo Plug to Two 3.5mm Mono Sockets Adaptor for £1.49, two of those will give you what you need, and they do several other headphone splitters, although all seem to assume a two way, rather than three way, split. Often these are sold as Ipod accesories. No doubt you can buy a platinum plated, oxygen free, oriented crystal, feng shuied version for under a grand if you care about audio quality ;->

Andy

[fred]

In article , Andy Dingley writes

I concur (ish), most little headphones appear to be 16ohms and all mfrs seem happy to let you use 2 way splitters so that means they can drive

8ohms ok, add another set in parallel again and you get 5.3ohms. My thoughts are that this is getting a bit close to the bone but the little amplifier feeding this will be protected against overload so unlikely to cause damage. If you wanted to be safe, you could add an 8.2ohm resistor to each feed (six in all) which would keep the impedance above 8ohms to the player when all 3 are paralleled. Loss in volume from the passive split would be about 4dB (I think :-) but use of good quality (efficient) headphones should still give the kids enough headroom to deafen themselves. Sony have some very efficient little phones and Argos 534/0466 11.99 have an on lead volume control, also Philips might be good enough (Argos 534-3463 3.99 again with vol control but no stock).

HTH

[Lobster]

Thanks to everyone for the replies.

I think I'll start by wiring two or three headphones in parallel just to see if it works, as it doesn't sound like it will do any harm, but failing that the above sounds like a good plan. Would be very grateful if you'd email me the spec sheet, Dave (the dodgy-looking return address on this post does work in fact).

Thanks David

[fred]

Data's here dave

, looks like it will drive down to 4ohms so provided you use phones with volume controls a single device would do the job.

[Lobster]

Ah, thanks.... ouch, think I'll be giving that one a miss though, that level of electrotrickery is a bit beyond my expertise!

David